1. Field of the Invention
The present invention relates to a technique preferably used as a sealing means of a chamber or the like used in a production of a semiconductor, a liquid crystal device or the like, and more particular, to a sealing structure for sealing by a seal ring which is installed in a dovetail groove formed at one of parts facing each other and provided between the parts with an appropriate deformable margin.
2. Description of the Conventional Art
A semiconductor production device or a liquid crystal product production device uses various vacuum treatment systems and carries out processing steps of a silicon wafer or a liquid crystal glass, which are needed for producing a semiconductor device, under a vacuum condition. FIGS. 7(A) to 7(C) are cross sectional views for illustrating plural kinds of sealing structures used in a conventional technique for sealing opening/closing portions such as a gate valve, a slit valve, a chamber lid and the like in a vacuum chamber so as to make such the vacuum condition.
In the sealing structures illustrated in FIGS. 7(A) to 7(C), FIG. 7(A) is a sealing structure in which an O ring 200 is installed in a dovetail groove 100 where both inner surfaces 101 and 102 at both sides are inclined to fall toward the inside of the groove 100 (for example, refer to Japanese Patent Application Laid Open No. 2003-240123 and Japanese Utility Model Laid Open No. 4 (1992)-127460). FIG. 7(B) is a sealing structure in which an O ring 200 is installed in a dovetail groove 110 where one inner surface 111 is inclined to fall toward the inside of the groove 110 and another inner surface 112 is vertically extended from a groove bottom 113. FIG. 7(C) is a sealing structure in which an O ring 200 is installed in a dovetail groove 120, where one inner surface 121 is inclined to fall toward the inside of the groove 120 and another inner surface 122 is vertically extended from a groove bottom 123, and a groove shoulder 124 at the inclined side bites the O ring 200.
As for the sealing structure in FIG. 7(A), the dovetail groove 100 is in the cross sectional shape where both inner surfaces 101 and 102 at both sides are inclined to fall toward the inside of the groove 100. So, an engagement allowance (W200−W100) generated by the difference between an opening width W100 of the dovetail groove 100 and a cross sectional width W200 of the O ring 200 is large. Thus, when the opposite member, which is not illustrated, is opened, it can be effectively prevented for the O ring 200 to come out of the dovetail groove 100 to slip off, even if the O ring 200 adheres to the opposite member. However, in the processing of the dovetail groove 100, a groove is formed by using a milling machine at first, and then, the inside of the groove is cut by an end mill so as to form the illustrated cross sectional shape. In this case, twice cutting processes are needed for the inner surface 101 and the inner surface 102 using a forming tool, so that there is a problem that a processing cost increases.
As for the dovetail groove 110 illustrated in FIG. 7(B), since only the inner surface 111 at one side is the inclined surface, the cutting process using the forming tool is needed only one time, and a lathe processing can be carried out, so that the groove 110 can be machined with a low cost. However, the engagement margin (W200−W100) of the O ring 200 to the dovetail groove 110 is small, and one side of the O ring 200 is not engaged. So, when the opposite member, which is not illustrated, is opened, the O ring 200 may easily come out of the dovetail groove 110 to fall off, if the O ring 200 adheres to the opposite member.
Further, as for the dovetail groove 120 illustrated in FIG. 7(C), since only the inner surface 121 at one side is the inclined surface like the dovetail groove 110 illustrated in FIG. 7(B), the groove 120 can be machined with a low cost. Further, since the O ring 200 is installed in the dovetail groove 120 in such manner that the groove shoulder 124 bites the O ring 200, a necessary engagement margin (W200−W100) of the O ring 200 to the dovetail groove 120 can be kept. Thus, the O ring 200 hardly comes out of the groove 120. However, the O ring 200 is forcibly passed between the groove shoulders 124 and 125 when it is fitted into the dovetail groove 120, and thus resistance of insertion is large and installation property is poor. Further, the structure of FIG. 7(C) has the flowing problems.
FIG. 8 illustrates the state where poor installation of the O ring 200 in the dovetail groove 120 occurs FIG. 7(C). As illustrated in FIG. 8, the O ring 200 is not completely inserted into the dovetail groove 120 due to the resistance of insertion with respect to the dovetail groove 120, so as to be waved. As a result of this, the state of uniform installation to the whole periphery cannot be obtained, so that sealing property may be unstable.
Further, FIG. 9 is an explanation view for illustrating an analysis result of stress distribution generated in the O ring 200 in the structure illustrated in FIG. 7(C) by an FEM analysis. In FIG. 9, a portion H has high stress, and a portion L has low stress. As illustrated in FIG. 9, when the O ring 200 receives a close contact load with the opposite member 130, the stress is remarkably increased at portions of the O ring 200 contacting to the groove shoulders 124 and 125 of the dovetail groove 120. Therefore, when the opposite member 130 is repeatedly opened and closed, the portions contacting to the groove shoulders 124 and 125 are abraded so as to easily generate particles which are harmful in the production of semiconductor and liquid crystal products. Further, the O ring 200 is waved at the time of inserting or due to opening/closing of the opposite member 130, so that sealing property may be unstable.